This invention relates to a stave cooler used for, cooling a furnace body by being attached to a furnace wall of a metallurgical furnace such as a blast furnace, an electric arc furnace and the like.
A stave cooler used as a cooling unit of a furnace wall of a metallurgical furnace such as a blast furnace and the like, becomes worn or broken through protracted use. When a stave cooler sustains such wear or breakage, its cooling ability lowers and heat loads on furnace shells increase, the increased heat loads leading to the occurrence of cracks in the furnace shells.
Generally speaking, a stave cooler is constructed in a manner in which,as shown in FIG. 7, cooling pipes 2 are embedded by casting in base metal (usually nodular graphite cast iron) forming the stave cooler proper 1 on the side opposite the furnace interior side and refractory bricks 9 are cast integrally on the furnace interior side as refractory materials. The stave cooler is fixed to the interior surface of a furnace shell 7 and refractory bricks 8 are piled on the furnace interior side of the stave cooler with stamp material 12 in-between.
A stave cooler of different structure has been proposed, wherein, instead of piling the refractory bricks, refractory bricks 10 are cast in the stave cooler proper 1 on the furnace interior side in a manner where the bricks 10 are supported, row by row, between ribs 11 of the base metal as shown in FIGS. 8(a) and 8(b).
The refractory bricks cast in the furnace interior side of the stave cooler have to be excellent in resistance against wear caused by the flow of high temperature gas and dropping of the material inside the furnace and in heat insulation ability to prevent a decrease in thermal efficiency caused by heat transfer from the furnace interior. The stave cooler thus functions, thanks to cooling water flowing through the cooling pipes, to cool, besides the furnace wall, the base metal and/or the refractory bricks on the furnace interior side so as to maintain their strength in reducing the rate of wear of the base metal and/or the refractory bricks caused by dropping of the material in the furnace, even when wear is accelerated by an increase in the heat load in the furnace interior.
However, the structure of the stave cooler shown in FIG. 7, where refractory bricks are piled on the furnace interior side, is unstable because there are no structural members to support the refractory bricks and they are supported only by the bonding strength of the binder between them. For this reason, the stave cooler of this structure has a problem in that the refractory bricks can fall out, locally or over the entire surface, in a hot and abrasive environment such as that in a blast furnace, and the service life as a refractory structure is drastically reduced as a result.
In addition, using the structure of the stave cooler shown in FIGS. 8(a) and 8(b), in which structure the refractory bricks are embedded in the base metal by casting, the force supporting the refractory bricks is weak, since they are supported only by the base metal ribs with a cushioning material (ceramic felt, etc.) placed in-between for preventing the bricks from cracking during casting of the stave. For this reason, a stave cooler of this structure is prone to a problem in which the refractory bricks fall out or break as a result of the change in the gaps between the ribs caused by thermal expansion/shrinkage during furnace operation.
If the refractory bricks thus fall out or break in an early stage of use leaving the base metal ribs behind, the furnace interior surface becomes irregular and, as a result, the dropping of the material in the furnace becomes discontinuous and unstable.
In addition, in order to minimize heat flux from the furnace interior, refractory bricks having a good heat insulation ability are chosen. If the refractory bricks fall out in an early stage of use, even locally, the stave cooler cannot maintain its heat insulation ability for a long period and, adversely, the heat loss tends to be increased by the influence of the ribs left protruding towards the furnace interior after the bricks have fallen out.
To solving this problem, Japanese Unexamined Patent Publication No. H8-120313 discloses a structure of a stave cooler in which columnar bricks having a round or polygonal section shape are arranged on the furnace interior side of the stave cooler perpendicularly to the surface and not contacting each other so that each of the bricks is wrapped around on all sides by the base metal, and Japanese Unexamined Patent Publication No. H5-320727 discloses another structure of a stave cooler in which refractory bricks, each positioned by a support anchor fitted into a tapered hole drilled through the brick near its center, are arranged in a zigzag pattern and embedded integrally in a base metal by casting.
However, when refractory bricks are arranged separately with a certain gap between them, each of them must be held to prevent from floating at casting and their positioning is difficult, and therefore, the manufacturing of the stave cooler requires a substantially long time.
The refractory bricks have also to be wrapped with a cushioning material such as ceramic felt or the like to prevent cracking resulting from heat shock during casting, but the work efficiency of the brick wrapping work piece by piece with the cushioning material is very. low.
In the structures described above, the chance of the refractory bricks falling out is small, since they are wrapped around by the base metal, but there still remains a possibility that they will crack or flake off as a result of thermal deformation of the stave cooler proper.
In addition to the above, Japanese Unexamined Utility Model Publication No. H6-47347 discloses two stave cooler structures: one using stainless steel blocks as a refractory material, dovetail grooves cut on the furnace interior side of the stave cooler proper, mortar applied inside the grooves to adjust gaps, and fitting and fixing of the stainless steel blocks having a tapered section shape into the grooves; and the other involving forming pits having a quadrilateral section shape on the furnace interior side of a stave cooler, fitting stainless steel blocks having a quadrilateral section shape into the pits and weld the furnace interior side surface of each block to the stave cooler proper.
In either case, however, the stainless steel blocks are fitted and fixed into the grooves or the pits of the stave cooler proper after its casting, and stainless steel blocks are heavier than bricks. For these reasons, the manufacturing work efficiency is very low.
Further, since stainless steel blocks having a tapered section are fitted in the dovetail grooves with mortar in-between for adjusting gaps, the strength of support for the blocks is weak and thus it is possible blocks will fall out owing to thermal deformation of the stave cooler proper.
Stainless steel blocks having a quadrilateral section, on the other hand, are supported only by the welding at the surface and thus it is possible the blocks will fall out like the tapered section stainless steel blocks, when the welded portions fracture due to the difference in the coefficient of thermal expansion of the stainless steel and the nodular graphite cast iron of the base metal or when they are worn by the dropping of the material.
In addition, manufacturing of the blocks is costly when they are made from rolled stainless steel materials.
The object of the present invention is to solve the above problems and provide, more economically, a stave cooler having a long service life and capable of maintaining heat insulation ability and wear resistance for a long period.
Thus, the gist of the present invention is as follows:
(1) A stave cooler to cool a furnace body, having a structure in which cooling pipes to cool a base metal are cast on the side opposite the furnace interior side of the base metal, characterized by casting a heat resistant steel plate having openings or a lamination of heat resistant steel plates having openings in the furnace interior side of the base metal.
(2) A stave cooler to cool a furnace body according to the item (1), characterized in that the heat resistant steel plate(s) having openings is/are a latticed or slotted heat resistant steel plate(s).
(3) A stave cooler to cool a furnace body according to the item (1) or (2), characterized in that the thickness of the heat resistant steel plate or that of the lamination of the steel plates is 3 mm or more and ⅔ or less of the thickness of the stave cooler.
(4) A stave cooler to cool a furnace body according to the item (1), (2) or (3), characterized in that, in the lamination of the heat resistant steel plates, the positions of the openings of a heat resistant steel plate are different from those of an adjacent heat resistant steel plate.
(5) A stave cooler to cool a furnace body according to the item (1), (2), (3) or (4), characterized in that the net volume of the heat resistant steel plate(s) is 20 to 60% of its/their gross volume, namely the sum of the net volume of the heat resistant steel plate(s) and the volume of the space of the openings.
(6) A stave cooler to cool a furnace body according to the item (1), (2), (3)1, (4) or (5), characterized in that the minimum width of the openings of the heat resistant steel plate(s) having openings is 30 mm or more and 70 mm or less.
(7) A stave cooler to cool a furnace body according to the item (1), (2), (3), (4), (5) or (6), characterized in that the heat resistant steel plate(s) is/are austenitic or ferritic heat resistant steel plate(s).
(8) A stave cooler to cool a furnace body, having a structure in which cooling pipes to cool a base metal are cast on the side opposite the furnace interior side of the base metal, characterized by forming a latticed or slotted heat resistant steel plate having openings or a lamination of latticed or slotted heat resistant steel plates having openings into a rectangular parallelepiped, and casting it, in a plurality, in the furnace interior side of the base metal.
(9) A stave cooler to cool a furnace body according to the item (8), characterized in that the thickness of the rectangular parallelepiped is 3 mm or more and ⅔ or less of the thickness of the stave cooler.
(10) A stave cooler to cool a furnace body according to the item (8) or (9), characterized in that, in said rectangular parallelepiped, the positions of the openings of a heat resistant steel plate are different from those of an adjacent heat resistant steel plate.
(11) A stave cooler to cool a furnace body according to the item (8), (9) or (10), characterized in that the net volume of the rectangular parallelepiped is 20 to 60% of its gross volume, namely the sum of the net volume of the heat resistant steel plate(s) and the volume of the space of the openings.
(12) A stave cooler to cool a furnace body according to the item (8), (9), (10) or (11), characterized in that in the rectangular parallelepiped the minimum width of the openings is 30 mm or more and 70 mm or less.
(13) A stave cooler to cool a furnace body according to the item (8), (9), (10), (11) or (12), characterized in that the heat resistant steel plate(s) is/are austenitic or ferritic heat resistant steel plate(s).